Self Propel Motor Making Strange Noises

I have had my EGO Self Propel lawn mower for about a year and a half. It does a great job and I really love this mower. Recently, the self propel motor is starting to make strange noises. It's not the normal whining that the electric motor makes. It's an additional noise to the normal whining. Is there some kind of self maintenance that has to be done with the self propel motor/gears?